Terphenyl Substituents Research Articles

A crystalline stannyne.

The synthesis of heteronuclear alkyne analogues incorporating heavier group 14 elements (R1-C≡E-R2, E = Si, Ge, Sn, Pb) has posed a long-standing challenge. Neutral silynes (R1-C≡Si(L)-R2) and germynes (R1-C≡Ge(L)-R2) stabilized by a Lewis base have achieved sufficient stability for structural characterization at low temperatures. Here we show the isolation of a base-free stannyne (R1-C≡Sn-R2) at room temperature, achieved through the strategic use of a bulky cyclic phosphino ligand in combination with a bulky terphenyl substituent. Despite an allenic structure with strong delocalization of π-electrons, this compound exhibits adjacent ambiphilic carbon and tin centres, forming a carbon-tin multiple bond with ionic character. The stannyne demonstrates reactivity similar to carbenes or stannylenes, reacting with 1-adamantyl isocyanide and 2,3-dimethyl-1,3-butadiene. Additionally, its carbon-tin bond can be saturated by Et3N·HCl or cleaved by isopropyl isocyanate.

Sterically Crowded Gold Germylene Compounds with Methyl and Hydride Substituents

AbstractThis work explores the combination of sterically crowded low‐valent germanium compounds bearing one or two terphenyl (C6H3‐2,6‐Ar2) substituents with gold fragments, the latter stabilized by crowded phosphines also containing a terphenyl moiety. The steric protection of these motifs has allowed to examine a series of unusual gold‐germylene compounds featuring small hydride and methyl substituents at the germanium site. A gold‐germylene dicationic structure is also reported. The bonding in this series is investigated by computational means, providing understanding for the two‐way transfer of electrons from germanium to gold and vice versa.

A series of ferriostannylenes with differing terphenyl substituents

A series of ferriostannylenes of formula ArMe6SnFeCp(CO)2 (ArMe6 = −C6H3-(C6H2–2,4,6-Me3)2, Cp = η5-C5H5) (1), ArMe6SnFeCp*(CO)2 (Cp* = η5-C5Me5) (2), and ArMe6SnFeCp(CO)(PMe3) (3) with differing iron and/or tin substituents was synthesized. Their structures and spectroscopic properties were examined by X-ray crystallography, NMR, IR, and UV–vis spectroscopy and compared with data for related species. The structural data showed that, as the size of the terphenyl substituent increases, the C-Sn-Fe angle decreases slightly which is contrary to steric expectations. The 1H and 119Sn NMR chemical shifts of the least crowded species 1 is similar to, but slightly upfield of those of its more hindered ferriostannylene analogs. Unexpectedly, 3 displayed a 119Sn NMR chemical shift that is ca. 800 ppm downfield of 1 as a result of the substitution of one of the iron carbonyl groups with a PMe3 ligand. This unusual finding is probably a reflection of a decreased paramagnetic shielding of the 119Sn nucleus by the more electron releasing character of the PMe3 ligand which decreases the n→p energy gap. The infrared spectrum of 1 also displayed slightly higher νCO frequencies, and its electronic spectrum indicated a small hypsochromic shift in the energy of its n→p transition whereas both 2 and 3 displayed much greater hypsochromic shifts than 1 consistent with the more electron donating character of the iron phosphine substituent. The results were interpreted in terms of the electronic/steric properties of the various substituents and their effects on metal electron density.

Generation of a transient base-stabilised arylalumylene for the facile deconstruction of aromatic molecules.

While a stable base-free arylalumylene bearing a sterically encumbered terphenyl substituent has been reported previously, we herein report that our attempts to form a base-stabilised arylalumylene bearing a relatively small terphenyl substituent and an N-heterocyclic carbene base led instead to a “masked” dialumene (LRAl Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> AlRL), self-stabilised by one peripheral aromatic group. Intriguingly, examining the behavior of this species or its transient dialumene formed from reducing the diiodoarylalane in aromatic solvents under different conditions reveals that they both decouple into the desired base-stabilised arylalumylene. This transient acyclic, dicoordinate alumylene is highly reactive, deconstructing benzene and toluene to furnish dialuminium derivatives of pentalene, providing the first example of a neutral AlI compound able to deconstruct these less reactive arenes. Computational insights were also gained on the dialumene dissociation and on the mechanism of arene deconstruction by alumylene.

Dimeric Copper and Lithium Thiolates: Comparison of Copper Thiolates with Their Lithium Congeners.

The direct reactions of the large terphenyl thiols HSAriPr4 (AriPr4= -C6H3-2,6-(C6H3-2,6-iPr2)2) and HSAriPr6 (AriPr6= -C6H3-2,6-(C6H2-2,4,6-iPr3)2) with stoichiometric amounts of mesitylcopper(I) in THF at ca. 80 °C afforded the first well-characterized dimeric copper thiolato species {CuSAriPr4}2 (1) and {CuSAriPr6}2 (2) with elimination of mesitylene. The complexes 1 and 2 were characterized by NMR and electronic spectroscopy as well as by X-ray crystallography. They have dimeric Cu2S2 core structures in which the two copper atoms are bridged by the sulfurs from the thiolato ligands and feature short Cu--Cu distances near 2.4 Å as well as a weak copper-flanking aryl ring interaction from a terphenyl substituent. The structures of the planar Cu2S2 cores bear a resemblance to the CuA site in nitrous oxide reductase in which two cysteines also bridge two copper atoms. The related dimeric Li2S2 structural motif was also observed in the lithium congeners {LiSAriPr4}2 (3) and {LiSAriPr6}2 (4) which were synthesized directly from the thiols and n-BuLi in hexanes. However, despite the very similar effective ionic radii of the Li+ (0.59 Å) and Cu+ (0.60 Å) ions, the Li--Li structures display very much longer (by more than ca. 0.5 Å) separations than the corresponding Cu--Cu distances in 1 and 2, which may be due to weaker dispersion interactions.

Isolable Phospha- and Arsaalumenes.

The combination of (AlCp*)4, a source of monomeric :AlCp* at elevated temperatures, with DipTerPnPMe3 (Pn = P, As), so-called pnicta-Wittig reagents, at 80 °C cleanly gives the pnictaalumenes DipTerPnAlCp* with polarized Pn-Al double bonds and intramolecular stabilization through interactions of Al with a flanking aryl group of the terphenyl substituent on Pn. In contrast, using MesTerPPMe3, the reaction with 2 equiv of :AlCp3t or :AlCp* afforded the three-membered 2π-aromatic ring systems MesTerP(AlCpx)2 (x = 3t, *).

A Tale of Biphenyl and Terphenyl Substituents for Structurally Diverse Ketiminato Magnesium, Calcium and Germanium Complexes.

In this paper, we have used two N,O-ketiminato ligands (L1 and L2) with biphenyl and terphenyl substituent on the nitrogen atom. Deprotonation of L1 with KN(SiMe3 )2 and subsequent reaction with MgI2 led to a homoleptic dinuclear magnesium complex (1) with a Mg2 O2 four-membered ring. Deprotonation with nBuLi and subsequent reaction with MgI2 afforded a unusual dinuclear magnesium complex (2) with a Mg2 O2 ring. Extension of the ligand for calcium resulted in a trinuclear calcium complex (3) with six four-membered Ca2 O2 rings. We could not isolate any chelating complex when L2 was used as a ligand, and only oxygen bound magnesium (4) and calcium (5) adducts were isolated. DFT studies were performed to understand this dissimilar behavior. More diverse results were obtained when lithiated L1 and L2 were treated with germanium dichloride. We were able to stabilize a monomeric germylene monochloride (7) with L1. However, with L2, an unusual ligand scrambling, and a C-C coupling take place, leading to the formation of a secondary carbocation with GeCl3 - as a counter-anion (8). Besides, a germanium dichloride adduct (9) bound to the oxygen center of the ligand was obtained as the minor product.

Ge=B π-Bonding: Synthesis and Reversible [2+2] Cycloaddition of Germaborenes.

Phosphine‐stabilized germaborenes featuring an unprecedented Ge=B double bond with short B⋅⋅⋅Ge contacts of 1.886(2) (4) and 1.895(3) Å (5) were synthesized starting from an intramolecular germylene–phosphine Lewis pair (1). After oxidative addition of boron trihalides BX3 (X=Cl, Br), the addition products were reduced with magnesium and catalytic amounts of anthracene to give the borylene derivatives in yields of 78 % (4) and 57 % (5). These halide‐substituted germaborenes were characterized by single‐crystal structure analysis, and the electronic structures were studied by quantum‐chemical calculations. According to an NBO NRT analysis, the dominating Lewis structure contains a Ge=B double bond. The germaborenes undergo a reversible, photochemically initiated [2+2] cycloaddition with the phenyl moiety of a terphenyl substituent at room temperature, forming a complex heterocyclic structure with GeIV in a strongly distorted coordination environment.

Evaluating stereoelectronic properties of bulky dialkylterphenyl phosphine ligands

The stereoelectronic properties of a series of sterically hindered phosphines containing a terphenyl substituent, PR2Ar’ (R = alkyl; Ar’ = C6H3-2,6-Ar2), have been evaluated by various methods. Their σ-donating capacity has been assessed on the basis of the carbon monoxide stretching frequencies in benchmark iridium [IrCl(CO)2(PR2Ar’)] and rhodium [Rh(acac)(CO)2(PR2Ar’)] (acac = acetylacetonate) complexes, as well as by measuring 31P–77Se scalar coupling constants (1JSeP) for the corresponding phosphine selenides (Se=PR2Ar’). In turn, the steric profile of terphenyl phosphines has been gauged by calculating Tolman Cone Angle (TCA), ligand shielding (G) and percent buried volume (%VBur) parameters. These calculations have been carried out from both X-ray diffraction and DFT-optimized structures. We have also examined several of the widely used biaryl phosphines for comparative purposes.

Counterintuitive Interligand Angles in the Diaryls E{C6H3-2,6-(C6H2-2,4,6-iPr3)2}2 (E = Ge, Sn, or Pb) and Related Species: The Role of London Dispersion Forces

The straightforward reaction of two equivalents of the lithium salt of the bulky terphenyl ligand Li(OEt2)C6H3-2,6-(C6H2-2,4,6-iPr3)2 with suspensions of GeCl2·dioxane, SnCl2, or PbBr2 in diethyl ether resulted in the isolation of the very crowded σ-bonded diaryl tetrylenes of formula E{C6H3-2,6-(C6H2-2,4,6-iPr3)2}2 (E = Ge (1), Sn (2), Pb (3)) as blue crystalline solids. Despite their high level of steric congestion, X-ray crystallography showed that compounds 1–3 possess Cipso–E–Cipso interligand bond angles in the range 107.61–112.55°, which are narrower than those observed in analogous species with less bulky terphenyl substituents. Compounds 1–3 were characterized by 1H, 13C{1H} (1–3), and 119Sn{1H} (2) NMR spectroscopy, whereas solution 207Pb{1H} NMR spectroscopy of 3 has not yet afforded a signal under ambient conditions. FT-IR and UV–vis spectra of 1–3 were also recorded. The relatively narrow interligand angles displayed by 1–3 are attributed in part to the increase in London dispersion force int...

Ligand Rearrangement and Hemilability in Rhodium(I) and Iridium(I) Complexes Bearing Terphenyl Phosphanes

The synthesis of a series of cationic rhodium(I) and iridium(I) compounds stabilized by sterically demanding phosphanes that contain a terphenyl substituent PMe2Ar′ (Ar′ = 2,6‐diarylphenyl) is described. Salt metathesis of metal precursors [MCl(COD)(PMe2Ar′)] (M = Rh, Ir; COD = cyclooctadiene) with NaBArF {BArF = B[3,5‐C6H3(CF3)2]4} resulted in a series of cationic complexes in which the loss of the chlorido ligand is compensated by the appearance of relatively weak π interactions with one of the flanking aryl rings of the terphenyl substituent. The same experiments carried out with carbonyl complexes [MCl(CO)2(PMe2Ar′)] led to the corresponding cationic carbonyl complexes, the CO‐induced rearrangement reactivity of which was investigated, both experimentally and computationally. The differences in reactivity between rhodium and iridium complexes and as a result of varying the sterics of terphenyl phosphanes are discussed.

Cyclic Distannene or Bis(stannylene) with a Ferrocenyl Backbone: Synthesis, Structure, and Coordination Chemistry.

1,1'-Dilithioferrocene was reacted with 2 equiv of isopropyl (Ar*) or methyl (Ar') substituted terphenyl tin(II) chloride. Reaction product 1, carrying the bulkier terphenyl substituent Ar*, displays a bis(stannylene) structure in the solid state without formation of a tin-tin bond. Temperature-dependent solution 119Sn NMR spectroscopy, however, revealed a dynamic interplay between bis(stannylene) (100 °C) and cyclic distannene (-80 °C). In contrast to 1, the less bulky Ar' substituent results in a cyclic distannene 2. On the basis of temperature-dependent 119Sn NMR spectroscopy the Sn-Sn bond of compound 2 was preserved up to 100 °C. Both compounds were further characterized by solid-state 119Sn NMR spectroscopy as well as 119Sn and 57Fe Mössbauer spectroscopy. 1 reacted as a chelating ligand with nickel and palladium complexes [Ni(cod)2] and [Pd(nbe)3] (nbe = norbornene). In the resulting coordination compounds the nonstabilized stannylene acts as a donor as well as an acceptor ligand and shows a dynamic switch from donor to acceptor behavior in the monopalladium complex.

Anionic Polymerizations of Bis(terphenyl) Substituted Butadienes for Precursors of Head‐to‐Head Substituted Polyacetylenes

A series of butadiene derivatives with m‐(alkyl)terphenyl substituents at 2,3‐position is synthesized and used for anionic living polymerizations. The controllabilities of the polymerizations of these monomers depend on solvent, temperature, and the alkyl groups on the terphenyl rings. In tetrahydrofuran (THF), the polymerization does not occur or proceeds very slowly at −78 °C. In toluene or cyclohexane, the polymerization proceeds smoothly in the presence of a small amount of THF at 40 °C. Monomer with n‐butyl substituents on the phenyl ring undergoes polymerization in a well‐controlled manner in hydrocarbon solvent with or without THF additive. The resulting narrow disperse polybutadiene derivatives are characterized by using size exclusion chromatography, nuclear magnetic resonance spectroscopy, and ultraviolet spectroscopy. It is found that the polymer chains are formed almost exclusively by 1,4‐addition. The precursor polymers are converted into polyacetylenes with head‐to‐head regiospecificity by oxidative dehydrogenation using 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone. image

Synthesis, properties, and some rhodium, iridium, and platinum complexes of a series of bulky m-terphenylphosphine ligands

A series of sterically demanding aryl phosphine ligands (L) bearing terphenyl substituents, PR2Ar′ (R=hydrocarbyl, Ar′=2,6-diarylphenyl radical) has been prepared and characterized. The stability of these ligands towards oxidation in the air has been tested, and theoretical and experimental studies aimed to provide information on their electronic and steric properties have been performed. Treatment of the metal dimers [MCl(COD)]2 (M=Rh, Ir; COD=1,5-cyclooctadiene) with ligands PMe2ArXyl2 (L1) and PMe2ArDipp2 (L5), in a 1:1 metal:ligand ratio, afforded the expected square-planar 16-electron complexes [MCl(COD)(PMe2ArXyl2)] and [MCl(COD)(PMe2ArDipp2)], respectively. These compounds were readily converted into the corresponding dicarbonyl derivatives, [MCl(CO)2(PMe2ArXyl2)] and [MCl(CO)2(PMe2ArDipp2)], respectively. While the expected κ1-P coordination mode of the PR2Ar′ ligands is found for these rhodium and iridium species, the mononuclear Pt(II) derivative obtained by reaction of PtCl2 with PMe2ArDipp2 has composition [PtCl2(PMe2ArDipp2)], and exhibits a bidentate κ1-P, η1-arene coordination mode involving one of the ipso carbon atoms of a flanking terphenyl aryl ring. The corresponding carbonyl compound [PtCl2(CO)(PMe2ArDipp2)], was generated under a CO atmosphere and exhibits κ1-P coordination mode.

Reversibility in Reactions of Linker-Bridged Distannenes with Terminal Alkynes at Ambient Temperature.

The linker-bridged distannene [(2,6-Mes2)C6H3Sn]2C12H8 (1) featuring an acenaphthene linker and the sterically demanding terphenyl substituent Ar(Me) (= C6H3-2,6-Mes2; Mes = C6H2-2,4,6-Me3) was prepared and characterized by single-crystal analysis, NMR spectroscopy, as well as elemental analysis. Furthermore, the reactivity of distannene 1 and previously reported distannenes 2 and 3, bearing either a naphthalene or a 9,9-dimethylxanthene backbone and the terphenyl substituent Ar(Me), as well as bis(stannylene) 4, featuring a 9,9-dimethylxanthene backbone and the terphenyl substituent Ar(iPr) (= C6H3-2,6-Trip2; Trip = C6H2-2,4,6-i-Pr3), toward terminal alkynes at ambient temperature was investigated, leading to the formal [2 + 2] cycloaddition products 5-9. The reactions of distannene 1 with trimethylsilylacetylene and phenylacetylene, the reaction of distannene 2 with trimethylsilyl-acetylene, as well as the reaction of bis(stannylene) 4 with phenylacetylene show reversibility, while distannenes 2 and 3 react irreversibly with phenylacetylene at room temperature. A van't Hoff analysis of variable-temperature (1)H NMR spectra of the cycloadduct of the reaction of distannene 1 with trimethylsilylacetylene afforded a dissociation enthalpy (ΔHdiss) of 71.6 kJ·mol(-1), which is in surprisingly good agreement with the results of accompanying DFT calculations (ΔHdiss = 70.9 kJ·mol(-1)).

Hydroalumination of Alkenes and Alkynes by Primary Aluminum Hydrides under Mild Conditions

The reactions of the sterically crowded primary alane (ArPri8AlH2)2 (ArPri8 = C6H-2,6(C6H2-2,4,6-Pri3)2-3,5-Pri2) with alkynes and alkenes are described. It is shown that hydroalumination of the terminal alkynes HCCSiMe3 and HCCPh readily occurs under mild conditions via the cis-addition of the Al–H moiety across the CC triple bond with no evidence of hydrogen elimination. Hydroalumination was observed also with a range of terminal olefins, but no reactivity was observed with internal alkenes or alkynes. The relatively high reactivity of (ArPri8AlH2)2 was attributed to the steric crowding of the large terphenyl substituent, which favors dissociation of the alane and increases the availability of the more reactive three-coordinate aluminum site in the monomer. In keeping with this view, studies of the reactions of the three primary alanes (ArPri8AlH2)2, (ArPri4AlH2)2 (ArPri4 = C6H3-2,6(C6H3-2,6-Pri2)2), and (ArMe6AlH2)2 (ArMe6 = C6H3-2,6(C6H2-2,4,6-Me3)2) with alkenes showed that the reaction rates are inv...

Molecular tailoring: a possible synthetic route to hexasilabenzene

The possible synthesis of hexasilabenzene was studied as the consecutive reaction of three disilyne units in order to find a suitable substituent. Although there is a reaction pathway which leads to hexasilabenzene in the case of hydrogen (A) and phenyl (B) groups, and it is thermodynamically and kinetically favourable, the reaction can easily proceed toward octasila species which makes it impossible to keep the synthesis under control and prepare hexasilabenzene. In contrast to this, using a methylated terphenyl (D) substituent, the addition of the third disilyne unit to the four-membered silicon ring (D5) is highly unfavourable because of the steric hindrance of the substituents. The terphenyl group (C), however, seems to be a perfect substituent because the reaction pathway leading to substituted hexasilabenzene consists of thermodynamically favourable steps and small activation barriers, and further reaction is hindered by the bulky substituents. We suggest synthesizing hexasilabenzene from terphenyl-halosilanes, performing reductive dehalogenation.

Synthesis and Characterization of the Titanium Bisamide Ti{N(H)AriPr6}2(AriPr6= C6H3-2,6-(C6H2-2,4,6-iPr3)2and Its TiCl{N(H)AriPr6}2Precursor: Ti(II) → Ti(IV) Cyclization

The titanium bisamido complex Ti{N(H)Ar(iPr6)}2 (Ar(iPr6) = C6H3-2,6-(C6H2-2,4,6-(i)Pr3)2 (2), along with its three-coordinate titanium(III) precursor, TiCl{N(H)Ar(iPr6)}2 (1), have been synthesized and characterized. Compound 1 was obtained via the stoichiometric reaction of LiN(H)Ar(iPr6) with the Ti(III) complex TiCl3·2NMe3 in trimethylamine. Reduction of 1 with 1 equiv of KC8 afforded Ti{N(H)Ar(iPr6)}2 (2) in moderate yield. Both 1 and 2 were characterized by X-ray crystallography, NMR, and IR spectroscopy, magnetic studies, and by density functional theory (DFT) computations. The precursor 1 has quasi-four-coordinate coordination at the titanium atom, with bonding to two amido nitrogens and a chlorine as well as a secondary interaction to a flanking aryl ring of a terphenyl substituent. Compound 2 displays a very distorted four-coordinate metal environment in which the titanium atom is bound to two amido nitrogens and to two carbons from a terphenyl aryl ring. This structure is in sharp contrast to the expected two-coordinate linear structure that was observed in its first row metal (V-Ni) analogues. Magnetic studies confirm a d(1) electron configuration for 1 but indicate that Ti{N(H)Ar(iPr6)}2 (2) is diamagnetic at ambient temperature consistent with the oxidation of titanium to Ti(IV). The different structure of 2 is attributed to the high reducing tendency of the Ti(II) in comparison to the other metals.

The N,N‐Bis(terphenyl)aminophosphenium Cation – A Sensitive Probe for Interactions with Different Anions

AbstractA series of salts that contain the terphenyl‐substitutedbis(amino)phosphenium cation with different anions (F–,Cl–, [CF3CO2]–, [CF3SO3]–, [B(C6F5)4]–, [GaCl4]–, [SbF6]–, [Al{OCH(CF3)2}4]– and [CHB11H5Br6]–) has been prepared by different synthetic protocols. All of the products have been characterised spectroscopically and by single‐crystal X‐ray diffraction studies. A detailed analysis of the interionic interactions and their influence on the molecular structure of the phosphenium cation reveals a strong dependence on the capability of the anion to enter the pocket generated by the bulky terphenyl substituents.

Entropy-controlled thermal back-reaction of photochromic [2.2]paracyclophane-bridged imidazole dimer

A [2.2]paracyclophane-bridged imidazole dimer having bulky 3′,4′,5′-triphenyl-1,1′:2′,1″-terphenyl substituents was synthesized and the photochromic properties were investigated. The half-life of the colored species generated by the UV irradiation of the parent imidazole dimer was 1.0 ms at 298 K in benzene. Although such bulky substituents are introduced on the imidazole dimer, the fast thermal back-reaction can be observed as found in other [2.2]paracyclophane-bridged imidazole dimers. Herein, enthalpy and entropy of the activation energies (∆ H ‡ and ∆ S ‡, respectively) for the thermal back-reaction of the present molecule were compared with other [2.2]paracyclophane-bridged imidazole dimers in order to investigate the generality and the limitation of the molecular design of the photochromic imidazole dimer along with the correlation between bulkiness of the substituents and the rate constant of the thermal back-reaction. Finally, we referred to a new method for controlling the rate constant of the thermal back-reaction of [2.2]paracyclophane-bridged imidazole dimers.